A stuffy nose and headache are common symptoms of many illnesses. So how can you tell whether the culprit is a sinus infection, a common cold, or allergies when the symptoms of these three conditions are so similar?

“It can sometimes be difficult even for doctors to differentiate,” says Alan B. Goldsobel, MD, an allergist at Allergy and Asthma Associates of Northern California and an adjunct associate professor at Stanford University Medical Center in Stanford, California. But there are some key differences that can give you some clues. Get to know more about the symptoms of these three conditions to help you pinpoint the cause of your sinus congestion:

A Sinus Infection

  • What it feels like: Sinus congestion can cause an aching sensation and a feeling of fullness in the middle of your face, says Dr. Goldsobel. A sinus infection may also be accompanied by other symptoms like post-nasal drip, green (or yellow) nasal discharge, aching in your teeth, fever, bad breath, and sinus pressure or a headache that worsens when you lean forward or lie down. Your face may also feel tender, and upon examination, a doctor should be able to see pus draining near the sinuses, says Fuad M. Baroody, MD, a professor of surgery and pediatrics and director of pediatric otolaryngology at the University of Chicago Medicine and Biological Sciences in Chicago, Illinois.
  • What triggers it: Bacteria or viruses trigger sinus infections. Colds, allergies, asthma, and other health conditions can also cause them.
  • How long it lasts: Sinus infections may clear up on their own without treatment, but some might require medication. If your symptoms last for longer than seven to 10 days, your doctor may consider prescribing antibiotics.

A Cold

  •  What it feels like: You can expect a stuffy nose, but also some runny, discolored mucus, Goldsobel explains. You may also experience a sore throat, cough, sneezing, headache, or fatigue. Another sign is a rising temperature: Colds often trigger a fever, he says, but sometimes those fevers are so mild that people think they have allergies instead.
  • What triggers it: A virus.
  • How long it lasts: People usually fend off the cold virus (without treatment) within seven to 10 days, Baroody says. But if your symptoms have lingered past that window of time, you might have sinusitis. If you suspect you have a sinus infection, you should talk to your doctor.

An Allergic Reaction

  • What it feels like: You may experience some nasal congestion with allergies, but it usually accompanies a runny nose (clear, watery discharge), sneezing, and itchy nose and eyes. Allergies never cause a fever, Goldsobel notes.
  • What triggers it: Allergens cause an allergic reaction. Common indoor allergens include mold, dust, and animal dander, while outdoor triggers include pollen and ragweed.
  • How long it lasts: If you have seasonal allergies, you may struggle with allergy symptoms throughout the spring and fall, Dr. Baroody says. If you’re allergic to indoor allergens, you may experience symptoms year-round.

How to Treat Congestion

Because sinus infections, colds, and allergies share some similar symptoms, including congestion, medications like nasal sprays, oral antihistamines, and eye drops can help minimize your discomfort.

If allergies are to blame, do your best to avoid your known triggers and steer clear of any other potential irritants, such as smoke or air pollution. Long-term treatments like immunotherapy (allergy shots) can help desensitize you to allergens and improve symptoms over time.

When Colds and Allergies Cause Sinus Infections

Even if your sinus congestion is being caused by allergies or a cold, it doesn’t mean you won’t develop a sinus infection later on.

In fact, when people have colds or allergies, the lining of the nose will swell up, which prevents mucus from draining properly — and that can then lead to sinusitis, says Goldsobel. People with allergies and asthma may be more vulnerable to sinusitis, though it’s not proven, Baroody says.

If you are at higher risk for sinus infections, you can take steps to prevent them. Don’t let allergy symptoms spiral out of control. And, Baroody says, be on the lookout “for the symptoms of sinus infections, and treat them promptly.”